1. Field of the Invention
The present invention relates to a circuit device in which a plurality of IC chips are stacked, and more particularly relates to a circuit device in which an IC chip having a fixed substrate potential is stacked in an upper layer.
2. Description of the Related Art
Along with high integration and downsizing of semiconductor integrated circuits, a stacked circuit device is one of configurations which draw attention as a high-integration IC.
FIG. 6 is a cross-sectional view showing a configuration of a conventional stacked circuit device.
A plurality of wirings 156 are provided on one surface of a substrate 150, and a first IC chip 151 is fixed thereto with an adhesive material 159 interposed therebetween. Moreover, a second IC chip 152 is stacked thereon with an insulating adhesive material 160 interposed therebetween. On surfaces of the respective IC chips 151 and 152, electrode pads (not shown) are provided, respectively, which are connected to the wirings 156 provided on the substrate 150 through bonding wires 153 or the like. The respective wirings 156 are connected to external terminals 154 such as solder balls, which are provided on a rear surface of the substrate 150, through through-holes TH provided in the substrate 150.
The IC chips 151 and 152, bonding wires 153, and wirings 156 are sealed and packaged by use of a sealing resin 155. This technology is described for instance in Japanese Patent Application Publication No. 2002-368189.
In the stacked circuit device as described above, fixing of the second IC chip 152 is performed by use of the adhesive material 160 such as a die-attach sheet and an insulating adhesive in order to insulate the second IC chip 152 from the first IC chip 151. Specifically, a substrate of the second IC chip 152 is mounted in a floating state.
However, for example, in the case where an IC chip used by fixing a substrate potential, such as a bipolar IC, is desired to be used as the second IC chip 152, if the second IC ship 152 is stacked in an upper layer, the substrate potential is set in a floating state. Accordingly, there arises a problem that sufficient characteristics cannot be obtained.
Thus, in a circuit device including an IC chip used with a fixed potential, such as the bipolar IC, the IC chip used with the fixed potential is disposed in a bottom layer in the case of stack packaging. Consequently, versatility of the stack packaging is limited.
Moreover, as to devices in which the stack packaging cannot be realized, the IC chip used with the fixed potential is disposed on an approximately planar surface, and the like. Thus, there also arises a problem that a mounting area is increased.